Some sound cards can easily go down to 5 Hz and below.
(Not usually to DC, though.) There are a lot of sound
card tests and specs at <www.pcavtech.com> that
may help.
Coincidentally, the latest Circuit Cellar magazine (#147,
Oct 2002) has an article on getting response down to DC,
by generating your signal as FM on some middling carrier
frequency, and building an outboard demodulator to
convert back to baseband. They were using it for EKG
signals in the DC to low kHz range.
Robert Masta
tech@daqarta.com
D A Q A R T A
Data AcQuisition And Real-Time Analysis
Shareware from Interstellar Research
www.daqarta.com